This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Introduction During the planning stage of MRI-guided focused ultrasound treatments in breast, the actual location of the focus is verified by visualization of a low temperature test spots using proton resonance frequency (PRF) thermometry. However, in fat PRF becomes unreliable. The alternative approaches are based on T1-weighted imaging with fast spin-echo (FSE) [1] and on displacement imaging with MR-ARFI. The goal of this study was to evaluate both methods in human ex vivo breast tissue. Methods For six focal locations, imaging was performed with ultrasound, using MR-ARFI and FSE. For FSE, repetition time (TR) was varied. Imaging was performed on a 3T MRI scanner equipped with a HIFU system, and timed such that the sonications and the scans ended at the same time. SNR of the signal at the focus was analyzed using MR-ARFI displacement maps and FSE magnitude difference images. To read about other projects ongoing at the Lucas Center, please visit http://rsl.stanford.edu/ (Lucas Annual Report and ISMRM 2011 Abstracts)